Various techniques have been used for detecting defects in metal flowlines. “Pigs” have been pumped through pipe liner for decades to of detect corrosion or cracks in the pipeline. The method and operation of a detection tool is considerably different, however, for oilfield applications, wherein the tubulars are conventionally inspected after they have been disassembled from the tubular string. Oilfield tubulars descend in a generally vertical direction within a well, and various types of connections are used to couple oilfield tubulars, thereby creating various types of problems when a sensor passes by an interface. Pipeline sections are conventionally welded and “smart pigs” are pumped through pipelines of a considerable distance to detect defects.
U.S. Pat. No. 6,904,818 discloses a device for detecting defects in a riser with ultrasonic transducers. The unit is self-propelled, and a portion of the inspection unit is rotatable relative to the remainder of the unit. Sensor shoes are moved between a retracted and an extended position by pneumatic cylinders or by outwardly biased springs. The inspection unit travels to a selected location, stops, and takes a measurement, preferentially with the shoe, in direct contact with the well. The inspection unit is intended to take measurements only when the unit is at a fixed location in the pipeline.
U.S. Pat. Nos. 7,082,822 and 7,234,347 disclose an improved device compared to the '818 patent for inspecting a riser. The sensors are enclosed in a vessel, which is run in on a wireline. The housing provides the protection for the internal sensor components. An acoustic liquid is provided so that signals travel through metal components, through acoustic fluid, through a metal component, and in some cases through another acoustic fluid and another metal component, before the signals reach the target.
The disadvantages of the prior art are over come by the present invention, and a new non-destructive inspection technique is hereinafter disclosed for reliably protecting oilfield tubulars while the tubular remains in the well.